Naphthenic acids (HA) are a mixture of several cyclopentyl and cyclohexylcarboxylic acids with a molecular weight of 120 to 700 or more units of atomic mass. The main fraction is carboxylic acids with a carbon skeleton of 9 to 20 carbon atoms. Scientists claim that naphthenic acids (HA) are cycloaliphatic carboxylic acids with 10-16 carbon atoms, although acids containing up to 50 carbon atoms have been discovered in heavy oil.
Etymology
The term has roots in the somewhat archaic term “naphthene” (cycloaliphatic, but non-aromatic), which is used to classify hydrocarbons. It was originally used to describe a complex mixture of petroleum-based acids, when the analytical methods available in the early 1900s could only accurately identify a few naphthenic type components. Today, naphthenic acid is used in a more general sense to denote all carboxylic acids present in oil (whether cyclic, acyclic or aromatic compounds) and carboxylic acids containing heteroatoms such as N and S. Numerous studies have shown that most cycloaliphatic acids also contain straight and branched chain aliphatic acids and aromatic acids. Some acids contain> 50% combined aliphatic and aromatic acids.
Formula
Naphthenic acids are represented by the general formula CnH2n-z O2, where n is the number of carbon atoms and z is the homologous series. The value of z is 0 for saturated acyclic acids and increases to 2 in monocyclic acids, to 4 in bicyclic acids, to 6 in tricyclic acids, and to 8 in tetracyclic acids.
Acid salts, called naphthenates, are widely used as hydrophobic sources of metal ions in various applications. Aluminum and sodium salts of naphthenic acid and palmitic acid were combined during World War II to produce napalm. And napalm was successfully synthesized. The word napalm comes from the words naphthenic acid and palmitic acid.
Oil connection
The nature, origin, extraction and commercial use of naphthenic acid have been studied for quite some time. Crude oil from fields in Romania, Russia, Venezuela, the North Sea, China and West Africa is known to contain a large amount of acidic compounds compared to most American crude oil. The content of carboxylic acid in some California petroleum products is especially high (up to 4%), where cycloaliphatic and aromatic acids are reported to be the most common classes of carboxylic acids.
Composition
The composition varies depending on the composition of the crude oil and the conditions during refining and oxidation. Fractions that are rich in naphthenic acids can cause corrosion damage to refinery equipment, so the phenomenon of acid corrosion (NAC) is well understood. High acid crude oil is often referred to as high total acid number (TAN) crude oil or high acidity crude oil (HAC). Naphthenic acids are the main pollutant in water obtained from the extraction of oil from the oil sands of Athabasca (AOS). Acids have both acute and chronic toxicity to fish and other organisms.
Environmental aspect
In a frequently cited article published in Toxicological Sciences, Rogers stated that naphthenic acid mixtures are the most significant environmental pollutants from oil production from oil sands. In the worst-case scenario, they found that acute toxicity was unlikely for wild mammals exposed to acids in water, but repeated exposure could have adverse health effects.
In a 2002 article cited more than 100 times, Rogers et al reported a solvent-based laboratory procedure designed to efficiently extract acids from large volumes of water in the tailings pond (TPW) of Athabasca's oil sands. Naphthenic acids are present in AOS Tailings Water (TPW) at an estimated concentration of 81 mg / L, too low for TPW to be considered a viable source for commercial recovery.
Delete
Naphthenic acid is removed from petroleum substances not only to minimize corrosion, but also to extract commercially useful products. The greatest current and historical use of this acid is in the production of metal naphthenates. Acids are extracted from petroleum distillates by alkaline extraction, regenerated during acid neutralization, and then distilled to remove impurities. Acids sold commercially are classified by acid number, level of impurities and color. Used to produce metal naphthenates and other derivatives, such as esters and amides.
Naphthenates
Naphthenates are acid salts similar to the corresponding acetates, which are better defined but less useful. Naphthenates, like naphthenic acids in oil, are highly soluble in organic media such as paints. They are used in industry, including the production of such useful things: synthetic detergents, lubricants, corrosion inhibitors, additives for fuels and lubricants, wood preservatives, insecticides, fungicides, acaricides, wetting agents, napalm thickeners and oil driers used in painting and surface treatment of wood.
Oil sands
One study says that naphthenic acids are the most active environmental pollutants of all substances obtained as a result of oil production from oil sands deposits. However, under conditions of leakage and pollution, acute toxicity is unlikely for wild mammals exposed to acids in the water of a pond near the tailing dump, but repeated exposure may have adverse effects on animal health. Acids are present in oil sands and in water in tailings at an estimated concentration of 81 mg / L.
Using the Organization for Economic Co-operation and Development (OECD) protocols for toxicity testing, American researchers argued that, based on their studies, purified NKs when ingested were not acutely genotoxic to mammals. Nevertheless, damage caused by NK during short-term exposure during acute or intermittent exposure can accumulate upon repeated exposure.
Cyclopentane
Cyclopentane is a flammable alicyclic hydrocarbon with the chemical formula C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms, each of which is bonded to two hydrogen atoms above and below the plane. It is often presented as a colorless liquid with a smell similar to gasoline. Its melting point is -94 ° C, and the boiling point is 49 ° C. Cyclopentane belongs to the class of cycloalkanes and represents alkanes with one or more rings of carbon atoms. It is formed by cracking cyclohexane in the presence of alumina at high temperature and pressure.
The production of naphthenic acids, including cyclopentane, has lost its former mass in recent years.
It was first prepared in 1893 by the German chemist Johannes Wislikus. Recently, it is often referred to as naphthenic acids.
Role in production
Cyclopentane is used in the manufacture of synthetic resins and rubber adhesives, and also as a foaming agent in the manufacture of polyurethane insulating foam, which is found in many household appliances such as refrigerators and freezers, replacing environmentally harmful alternatives such as CFC-11 and HCFC- 141b.
Cyclopentane Multiple Alkylation Greases (MACs) have low volatility and are used in some specialized applications.
The United States produces more than half a million kilograms of this chemical per year. In Russia, naphthenic acids (including cyclopentane) are produced as a natural product of oil refining.
Cycloalkanes can be prepared using a process known as catalytic reforming. For example, 2-methylbutane can be converted to cyclopentane using a platinum catalyst. This is especially often used in cars, as branched alkanes will burn much faster.
Physical and chemical characteristics
Surprisingly, their cyclohexanes begin to boil 10 ° C higher than hexahydrobenzene or hexanaphthene, but this riddle was solved in 1895 by Markovnikov, N.M. Kishner and Nikolai Zelinsky when they reassigned hexahydrobenzene and hexanaphthene as methylcyclopentane - the result of an unexpected back-strike.
Although cyclohexane is quite unreactive, it undergoes catalytic oxidation to form cyclohexanone and cyclohexanol. A mixture of cyclohexanone-cyclohexanol, called "KA oil", is a raw material for adipic acid and caprolactam, nylon precursors.
Application
It is used as a solvent in some brands of correction fluid. Cyclohexane is sometimes used as a non-polar organic solvent, although n-hexane is still more widely used for this purpose. It is also often used as a solvent for recrystallization, since many organic compounds exhibit good solubility in hot cyclohexane and poor solubility at low temperatures.
Cyclohexane is also used to calibrate differential scanning calorimetry (DSC) instruments because of the convenient crystal-to-crystal transition at -87.1 ° C.
Cyclohexane vapors are used in vacuum cementation furnaces in the manufacture of heat treatment equipment.
Deformation
A ring with 6 vertices does not match the shape of a perfect hexagon. The conformation of a flat hexagon has a significant angular deformation, because its bonds do not amount to 109.5 degrees. Torsion deformation will also be significant, as all bonds will be eclipsed.
Therefore, in order to reduce torsional deformation, cyclohexane adopts a three-dimensional structure, known as a "conformational chair." There are also two other intermediate conformers - the “half chair”, which is the most unstable conformer, and the “twist boat,” which is more stable. These eccentric names were first proposed back in 1890 by Hermann Sachs, but were widely recognized much later.
Half of the hydrogen atoms are in the plane of the ring (equatorially), and the other half is perpendicular to the plane (axially). This conformation provides the most stable cyclohexane structure. There is another conformation of cyclohexane, known as a “conformation boat”, but it is converted to a slightly more stable formation of a “chair”.
Cyclohexane has the lowest angle and torsional deformation among all cycloalkanes, as a result of which cyclohexane is considered equal to 0 in the total ring deformation. The same is true for the sodium salts of naphthenic acids.
Phases
Cyclohexane has two crystalline phases. The high-temperature phase I, stable between +186 ° C and a melting point of +280 ° C, is a plastic crystal, which means that the molecules retain a certain degree of freedom of movement. The low temperature (below 186 ° C) phase II is more ordered. The other two low-temperature (metastable) phases III and IV were obtained by applying moderate pressures above 30 MPa, and phase IV appears exclusively in deuterated cyclohexane (note that the use of pressure increases the values of all transition temperatures).